Method and system for forming a workpiece

ABSTRACT

A method for shaping a workpiece having a base portion using a tool is provided. The method includes rotating the tool at a fixed rotational speed in a first direction and rotating the workpiece in the first direction. The tool is positioned in contact with the workpiece at a first portion of the base portion of the workpiece. The workpiece is rotated at a first rotational speed when the tool contacts the first portion of the base portion of the workpiece. The workpiece is rotated at a second rotational speed when the tool contacts a second portion of the base portion of the workpiece. The first rotational speed and the second rotational speed are different.

FIELD

The present disclosure relates to a grinding system, and moreparticularly to a grinding system configured to reduce grinding chatter.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

A common and useful method of shaping metal components is to use agrinding machine. A grinding machine typically includes a mounting forreceiving the workpiece and a grinding wheel for shaping the workpiece.Both the workpiece and the grinding wheel are rotated at predefinedworkspeeds to maximize efficiency.

For workpieces that have simple shapes, a constant rotational speed isemployed. For workpieces that require lobes or ramps, such as, forexample, camshafts used in motor vehicle engines, the rotational speedof the workpiece must be reduced in non-regular shaped areas. However,using a constant speed requires that the workpiece be formed at thelowest allowable rotational speed. This reduces efficiency and thenumber of parts that can be manufactured. One solution is to vary thespeed of the workpiece such that the workpiece rotates slower atnon-regular shaped areas and faster in regular shaped areas.

However, grinding systems using these variable speeds can still producevibrations that are difficult to control. These vibrations are caused byimbalances in the grinding system, such as, for example, by the grindingwheel imbalance, by the grinding wheel being out of roundness, or bygrinding wheel or spindle axial misalignment. These imbalances result ina surface that has grinding chatter. The frequency of the chatter is arelationship between the workpiece speed and the grinding wheel speed.For example, a 10,000 RPM grinding wheel speed and a 50 RPM workpiecerotation speed would make a chatter frequency of 200 undulations perrevolution. This chatter can cause machine damage and result in unevenworkpiece grinding, which in turn can increase engine noise in a motorvehicle if the workpiece is a camshaft. Accordingly, there is room inthe art for an improvement in reducing grinding chatter withoutsignificantly slowing grinding speeds.

SUMMARY

The present invention provides a method for shaping a workpiece having abase portion using a tool.

In a first aspect of the present invention, the method includes rotatingthe tool at a fixed rotational speed in a first direction and rotatingthe workpiece in the first direction. The tool is positioned in contactwith the workpiece at a first portion of the base portion of theworkpiece. The workpiece is rotated at a first rotational speed when thetool contacts the first portion of the base of the workpiece. Theworkpiece is rotated at a second rotational speed when the tool contactsa second portion of the base of the workpiece. The first rotationalspeed and the second rotational speed are different.

In another aspect of the present invention, the first portion is locatedat the beginning of a semi-circle on the base portion.

In still another aspect of the present invention, the second portion islocated at a middle of the semi-circle on the base portion.

In still another aspect of the present invention, the second rotationalspeed is greater or less than the first rotational speed.

In still another aspect of the present invention, the workpieceincreases rotational speed at a constant rate between the firstrotational speed and the second rotational speed.

In still another aspect of the present invention, the method furtherincludes the step of rotating the workpiece at a third rotational speedwhen the tool contacts a third portion of the base portion of theworkpiece.

In still another aspect of the present invention, the third portion islocated at an end of the semi-circle of the base portion.

In still another aspect of the present invention, the third rotationalspeed is equal to the first rotational speed.

In still another aspect of the present invention, the controllerdecreases rotational speed of the mounting portion at a constant ratebetween the second rotational speed and the third rotational speed.

The present invention further provides a system for shaping a workpiecehaving a semi-circular base portion.

In one aspect of the present invention, the system includes a rotatablemounting portion for receiving the workpiece therein, the rotatablemounting portion operable to rotate the workpiece, a rotatable grinderpositioned proximate to the mounting portion for contacting theworkpiece, and a controller in communication with the mounting portionand the grinder. The controller includes a memory with control logic.The control logic includes a first control logic for rotating thegrinder at a fixed rotational speed in a first direction, a secondcontrol logic for rotating the mounting portion in a second directionopposite the first direction, a third control logic for positioning thetool in contact with the workpiece at a first portion of the baseportion of the workpiece, a fourth control logic for rotating themounting portion at a first rotational speed when the tool contacts thefirst portion of the base portion of the workpiece, and a fifth controllogic for rotating the mounting portion at a second rotational speedwhen the tool contacts a second portion of the base portion of theworkpiece. The first rotational speed and the second rotational speedare different.

In another aspect of the present invention, the first portion is locatedat the beginning of a semi-circle on the base portion.

In still another aspect of the present invention, the second portion islocated at a middle of the semi-circle on the base portion.

In still another aspect of the present invention, the second rotationalspeed is greater than the first rotational speed.

In still another aspect of the present invention, the controllerincreases rotational speed of the mounting portion at a constant orvariable rate between the first rotational speed and the secondrotational speed.

In still another aspect of the present invention, the system includes asixth control logic for rotating the mounting portion at a thirdrotational speed when the tool contacts a third portion of the baseportion of the workpiece.

In still another aspect of the present invention, the third portion islocated at an end of the semi-circle of the base portion.

In still another aspect of the present invention, the third rotationalspeed can be equal to the first rotational speed.

In still another aspect of the present invention, the controllerdecreases rotational speed of the mounting portion at a constant orvariable rate between the second rotational speed and the thirdrotational speed.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic view of a grinding machine according to theprinciples of the present invention illustrated with an exemplaryworkpiece;

FIG. 2 is a side cross-sectional view of a portion of the grindingmachine and the exemplary workpiece taken in the direction of arrows 2-2in FIG. 1;

FIG. 3 is chart of the rotational speed of the exemplary workpiececorresponding to an angular position of the workpiece; and

FIG. 4 is a chart of the acceleration of the exemplary workpiececorresponding to an angular position of the workpiece.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

FIG. 1 illustrates a grinding system 10 according to the principles ofthe present invention. The grinding system 10 is shown with an exemplaryworkpiece 12. The grinding system 10 includes a mounting assembly 14, agrinding wheel 16, and a controller 18 in electronic communication withthe mounting assembly 14 and the grinding wheel 16.

In the particular example provided the workpiece 12 is a camshaft foruse in a motor vehicle, but it should be appreciated that the workpiece12 may take various forms without departing from the scope of thepresent invention such as, for example, fuel pump eccentrics. Theworkpiece 12 as illustrated includes a generally cylindrical body 18having a first end 20 and a second end 22. The workpiece 12 furtherincludes a plurality of cams 24 formed along the cylindrical body 18.The shape of the cylindrical body 18 and the cams 24 are formed byoperation of the grinding system 10, as will be described in furtherdetail below.

The mounting assembly 14 includes a first mounting portion 26 and asecond mounting portion 28. The first mounting portion 26 is adapted toreceive the first end 20 of the workpiece 12 therein. The secondmounting portion 28 is adapted to receive the second end 22 of theworkpiece 12 therein. In this way, the workpiece 12 extends between thefirst mounting portion 26 and the second mounting portion 28. The firstmounting portion 26 and the second mounting portion 28 are bothrotatable and are both operable in turn to rotate the workpiece 12.

A motor 30 is drivingly coupled to the second mounting portion 28. Themotor 30 is operable to rotate the second mounting portion 28 in a firstdirection “A”, which in turn rotates the workpiece 12 and the firstmounting portion 26 in the first direction “A”. It should be appreciatedthat the rotational direction “A” may be opposite to that indicated inFIG. 1 without departing from the scope of the present invention.

The mounting assembly 14 is coupled to a worktable (not shown) and ismoveable along an axis “X”. Movement of the mounting assembly 14 alongthe “X” axis allows the grinding system 10 to position the length of theworkpiece 12 relative to the grinding wheel 16.

The grinding wheel 16 includes a grinding disc 32. The grinding disc 32has a grinding surface 34 for engaging the workpiece 12 and removingmaterial therefrom. The grinding surface 34 is preferably roughened andformed from a tough material, such as, for example, carbon-boronnitrite, ceramic, or a conventional stone. In the particular exampleprovided, the grinding disc 32 is annular in shape, but it should beappreciated that the grinding disc 32 may have other shapes withoutdeparting from the scope of the present invention. The grinding wheel 16is drivingly connected to a motor (not shown) and is rotatable in thefirst direction “A”. Furthermore, the grinding wheel 16 is moveablealong an axis “Y”. Movement of the grinding wheel 16 along the “Y” axisallows the grinding system 10 to position the grinding wheel 16 suchthat it is in contact with the workpiece 12 and to allow the grindingwheel 16 to follow the shape of the workpiece 12.

The controller 18, as noted above, is in electronic communication withthe mounting assembly 14 and the grinding wheel 16. The controller 18 isan electronic device having a preprogrammed digital computer orprocessor, control logic, memory used to store data, and at least oneI/O section. The control logic includes a plurality of logic routinesfor monitoring, manipulating, and generating data. The controller 18 isoperable to send electronic control signals to the mounting assembly 14and the grinding wheel 16 in order to control the rotational speed ofthe workpiece 12 through the rotation of the second mounting portion 28,to control the position of the mounting assembly 14 along the “X” axis,to control the rotational speed of the grinding wheel 16, and to controlthe position of the grinding wheel 16 along the “Y” axis. To this end,the controller 18 includes a workspeed data file that containsinstructions for rotational speeds and grinder wheel 16 and mountingassembly 14 positions.

During operation of the grinding system 10, the grinding wheel 16 isrotated in the first direction “A” and the mounting assembly 14 in FIG.1 rotates the workpiece 12 in the first direction “A”. The grindingwheel 16 is rotated at a fixed rotational speed. The workpiece 12 isrotated according to the workspeed data table found in the memory of thecontroller 18. The controller 18 controls the position and rotationalspeed of the mounting assembly 14 and grinding wheel 16. When theworkpiece 12 and the grinding wheel 16 are in contact and in rotation,the grinding surface 34 removes material from the workpiece 12. Bypositioning the grinding wheel 16 along the “Y” axis, different amountsof material may be removed, thereby forming the base portion 36 and theramp portion 38. By positioning the workpiece 12 along the “X” axis,different sections of the workpiece 12 may be shaped.

Turning now to FIG. 2, a cross-section is illustrated of the workpiece12 at a cam 24 and of the grinding wheel 16. The cam 24 includes a baseportion 36 and a ramp portion 38. The base portion 36 is semi-circularin shape and includes a first portion 40, a second portion 42, and athird portion 44. The first portion 40 corresponds to the beginning ofthe semi-circle of the base portion 36. The second portion 42corresponds to the middle of the semi-circle of the base portion 36. Thethird portion 44 corresponds to the end of the semi-circle of the baseportion 36.

The ramp portion 38 includes a first flank 46, a second flank 48, and apoint 50. The first flank 46 extends from the first portion 40 of thebase portion 36 to the point 50. The second flank 48 in turn extendsfrom the third portion 44 of the base portion 36 to the point 50. Inthis way, the ramp portion 38 has a generally triangular shape.

FIG. 3 illustrates a chart 100 showing the preferred method of varyingthe rotational speed of the workpiece 12 with respect to the angularposition of the cam 24. This method of varying the rotational speed ofthe workpiece 12 is represented by line 102. The “x” axis of the chart100 is the angular position of the workpiece 12 with respect to contactwith the grinding wheel 16. Specifically, angular position “0” and “360”corresponds to the grinding wheel 16 contacting the point 50 in FIG. 2.Angular position “120” corresponds to the grinding wheel 16 contactingthe first portion 40 in FIG. 2. Angular position “180” corresponds tothe grinding wheel 16 contacting the second portion 42 in FIG. 2.Angular position “240” corresponds to the grinding wheel 16 contactingthe third portion 44 in FIG. 2. The “y” axis of the chart 100 is therotational speed of the workpiece 12 represented as a percentage of anominal workspeed. The nominal workspeed is a predefined constant speed.

In the preferred method of shaping the workpiece 12 of the presentinvention, the rotational speed of the workpiece 12 is varied betweenthe first portion 40 in FIG. 2 and the third portion 44 in FIG. 2.Specifically, when the grinding wheel 16 is positioned to contact theworkpiece 12 at the first portion 40, the workpiece 12 has a firstrotational speed, as indicated by reference numeral 104 on the line 102.As the workpiece 12 rotates, the grinding wheel 16 moves to contact thesecond portion 42 and the rotational speed of the workpiece 12 increasesto a second rotational speed, indicated by reference numeral 106 on line102. In the example provided, the second rotational speed is 30% greaterthan the first rotational speed, however, various other percentages maybe employed without departing from the scope of the present invention.Also in the example provided, the rotational speed of the workpiece 12increases at a constant rate, as indicated by the straight section onthe line 102 and indicated by reference numeral 108. Alternatively, therotational speed of the workpiece 12 may increase at a changing rate.

As the workpiece 12 continues to rotate, the grinding wheel 16 moves tocontact the third portion 44 and the rotational speed of the workpiece12 decreases from the second rotational speed at point 106 to a thirdrotational speed, indicated by reference numeral 110 on line 102. In theexample provided, the third rotational speed is equal to the firstrotational speed, though various other speeds may be employed so long asthe rotational speed of the workpiece 12 is not kept constant betweenfirst portion 40 and the third portion 44. In the preferred embodiment,the rotational speed of the workpiece 12 decreases at a constant rate,as indicated by the straight section on the line 102 and indicated byreference numeral 112. Alternatively, the rotational speed of theworkpiece 12 may decrease at a changing rate.

FIG. 4 illustrates a chart 200 showing the preferred acceleration of theworkpiece 12 with respect to the angular position of the cam 24. Thisacceleration of the workpiece 12 is represented by line 202. The “x”axis of the chart 200 is the angular position of the workpiece 12 withrespect to contact with the grinding wheel 16. Specifically, angularposition “0” and “360” corresponds to the grinding wheel 16 contactingthe point 50 in FIG. 2. Angular position “120” corresponds to thegrinding wheel 16 contacting the first portion 40 in FIG. 2. Angularposition “180” corresponds to the grinding wheel 16 contacting thesecond portion 42 in FIG. 2. Angular position “240” corresponds to thegrinding wheel 16 contacting the third portion 44 in FIG. 2. The “y”axis of the chart 200 is the acceleration of the workpiece 12.Acceleration changes are kept to a minimum by keeping the transitions ofworkpiece 12 rotation speed at points 104, 106, and 110 rounded.

By varying the rotational speed of the workpiece 12 during shaping ofthe base portion 36, the chatter is forced to have an inconsistentspacing. This in turn reduces the amplitude at any one particularfrequency of chatter, thereby reducing the chatter. At the same time,rotational speed is not reduced and therefore inefficiency is kept to aminimum.

The description of the invention is merely exemplary in nature andvariations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A method for shaping a workpiece using a tool, the workpiece having asemi-circular base portion, the method comprising: rotating the tool ata fixed rotational speed in a first direction; rotating the workpiece inthe first direction positioning the tool in contact with the workpieceat a first portion of the semi-circular base portion of the workpiece;rotating the workpiece at a first rotational speed when the toolcontacts the first portion of the semi-circular base portion of theworkpiece; and rotating the workpiece at a second rotational speed whenthe tool contacts a second portion of the semi-circular base portion ofthe workpiece; and wherein the first rotational speed and the secondrotational speed are different.
 2. The method of claim 1 wherein thefirst portion is located in a first half of the semi-circular baseportion.
 3. The method of claim 2 wherein the second portion is locatedin a second half of the semi-circular base portion.
 4. The method ofclaim 3 wherein the second rotational speed is greater than the firstrotational speed.
 5. The method of claim 4 wherein the workpieceincreases rotational speed at a constant rate between the firstrotational speed and the second rotational speed.
 6. The method of claim5 further comprising the step of rotating the workpiece at a thirdrotational speed when the tool contacts a third portion of thesemi-circular base portion of the workpiece.
 7. The method of claim 6wherein the third portion is located at an end of the semi-circular baseportion.
 8. The method of claim 7 wherein the third rotational speed isequal to the first rotational speed.
 9. (canceled)
 10. A system forshaping a workpiece, the workpiece having a semi-circular base portion,the system comprising: a rotatable mounting portion for receiving theworkpiece therein, the rotatable mounting portion operable to rotate theworkpiece; a rotatable grinder positioned proximate to the mountingportion for contacting the workpiece; a controller in communication withthe mounting portion and the grinder, the controller having a memorywith control logic, the control logic including a first control logicfor rotating the grinder at a fixed rotational speed in a firstdirection, a second control logic for rotating the mounting portion inthe first direction, a third control logic for positioning the tool incontact with the workpiece at a first portion of the semi-circular baseportion of the workpiece, a fourth control logic for rotating themounting portion at a first rotational speed when the tool contacts thefirst portion of the semi-circular base portion of the workpiece, and afifth control logic for rotating the mounting portion at a secondrotational speed when the tool contacts a second portion of thesemi-circular base portion of the workpiece; and wherein the firstrotational speed and the second rotational speed are different.
 11. Thesystem of claim 10 wherein the first portion is located in a first halfof the semi-circular base portion.
 12. The system of claim 11 whereinthe second portion is located in a second half of the semi-circular baseportion.
 13. The system of claim 12 wherein the second rotational speedis greater than the first rotational speed.
 14. The system of claim 13wherein the controller increases rotational speed of the mountingportion at a constant rate between the first rotational speed and thesecond rotational speed.
 15. The system of claim 14 further comprising asixth control logic for rotating the mounting portion at a thirdrotational speed when the tool contacts a third portion of thesemi-circular base portion of the workpiece.
 16. The system of claim 15wherein the third portion is located at an end of the semi-circular baseportion.
 17. The system of claim 16 wherein the third rotational speedis equal to the first rotational speed.
 18. The system of claim 17wherein the controller decreases rotational speed of the mountingportion at a constant rate between the second rotational speed and thethird rotational speed.